Fix OptStackOps label migration case for toscmpbool, add test case

src/cc65/coptstop.c

@@ -1153,6 +1153,8 @@ static unsigned Opt_a_toscmpbool (StackOpData* D, const char* BoolTransformer)
 
         /* Save lhs into zeropage */
         AddStoreLhsA (D);
+        /* AddStoreLhsA may have moved the OpIndex, recalculate insertion point to prevent label migration. */
+        D->IP = D->OpIndex + 1;
 
         /* cmp */
         X = NewCodeEntry (OP65_CMP, AM65_ZP, D->ZPLo, 0, D->OpEntry->LI);

test/val/bug1989.c

@@ -0,0 +1,40 @@
+
+/* bug #1989 - OptStackOps Opt_a_toscmpbool bypassed a comparison, discovered in 544a49c */
+
+#include <stdlib.h>
+
+unsigned char i,r,j;
+
+void fail() // for the r=0 case, the == comparison was getting jumped over by OptStackOps
+{
+    if ((i & 0x1f) == (r ? 0 : 16)) j -=8;
+}
+
+void pass()
+{
+    if ((i & 0x1f) == (unsigned char)(r ? 0 : 16)) j -= 8;
+}
+
+void test(unsigned char ti, unsigned char tr, unsigned char tj)
+{
+    unsigned char rj;
+    i = ti;
+    r = tr;
+    j = tj;
+    pass();
+    rj = j;
+    i = ti;
+    r = tr;
+    j = tj;
+    fail();
+    if (j != rj) exit(1);
+}
+
+int main(void)
+{
+    test( 1,0,33);
+    test( 0,0,33);
+    test( 1,1,33);
+    test(16,1,33);
+    return 0;
+}